Implement eslint and lint codebase

[DCSBL]

Continuing on #83

You thought #110 was big.. that was nothing...:

This PR:

• Implements eslint via the default config of https://github.com/athombv/eslint-config-athom
• Removes prettier (as this has conflicting rules, and was not used in CI)
• Adds a pre-commit-config file; Install pre-commit, and run pre-commit install. This runs some quick checks before each commit to prevent 'invalid' commits. Can be ignored via --no-check flag per commit or even not installed at all.

Real changes:

• package.json has a new 'scripts' to run eslint + addition of devDependencies
• Addition of pre-commit-config.yaml
• Updated eslintrc.json to use athoms style settings
• Updated validate.json to validate the change for each PR

The rest are auto-updated via eslint.

All non auto-fixable rules are disabled in eslintrc.json, and can be enabled step by step.

[jtebbens]

You are outmatching my coding skills. Lol

[DCSBL]

Hah, this is just some copy-pasta. I have no idea what I am doing actually 😇